Ursodeoxycholic acid is one type of bile acids found in bear bile, and has been known to have a cholagogic effect as its pharmaceutical activity. Tablets containing the compound are commercially available. However, as the compound is hardly soluble in water (38 .mu.g/ml), its use is limited. Improving its solubility in water will make the compound usable in injections, which may be applied even to postoperated-patients and to patients to whom drugs cannot be orally administered.
Accordingly, it is desired to develop a method for improving the solubility of ursodeoxycholic acid in water.
Known is glycosyiation as one means for improving the solubility of hardly-soluble substances.
For chemical glycosylation, various methods are known such as those described in Experimental Chemical Lectures 26, 4th Edition, "Organic synthesis VIII, Chapter 3", edited by the Chemical Society of Japan. However, all the known methods are disadvantageous for industrialization, as using strong Lewis acids. On the other hand, glycosylation with enzyme, if applied to ursodeoxycholic acid, is problematic in that only small amounts of products could be obtained as the solubility of the substrate, ursodeoxycholic acid in water is very low.